The Caribbean is a region of lush vegetation,
beaches, active volcanoes, and significant
mountain ranges, all of which create
a natural aesthetic that is recognized globally.
Yet these very same features, molded
through geological, oceanic, and atmospheric
processes, also pose natural hazards
for the developing countries in the Caribbean.
The rise in population density, migration
to coastal areas, and substandard building
practices, combined with the threat of
natural hazards, put the region’s human
population at risk for particularly devastating
disasters. These demographic and social
characteristics exist against a backdrop of
the threat of an evolving climate, which produces
a more vigorous hurricane environment
and a rising average sea level.
The 12 January 2010 earthquake in Haiti
and Hurricane Ike (2008) both caused widespread
destruction and loss of life, illustrating
the need for a scientific focus on the
underlying natural hazards of the Caribbean.
Prompted by these and other events,
a new National Science Foundation (NSF)–
funded initiative known as the Continuously
Operating Caribbean Observation Network
(COCONet), which commits roughly $7 million
over 5 years to a collaborative natural
hazard research team, was formed in
2010. This team includes researchers from
UNAVCO, Purdue University, University of
Puerto Rico at Mayagüez, and the University
Corporation for Atmospheric Research
(UCAR)

Newd13C data are presented from 10 coral skeletons
collected from Florida and elsewhere in the Caribbean
(Dominica, Dominican Republic, Puerto Rico, and Belize).
These corals range from 96 to 200 years in age and were
collected between 1976 and 2002. The change in the d13C
of the skeletons from these corals between 1900 and 1990
has been compared with 27 other published coral records
from the Atlantic, Pacific, and Indian Oceans. The new
data presented here make possible, for the first time, a
global comparison of rates of change in the d13C value of
coral skeletons. Of these records, 64% show a statistically
significant (p < 0.05) decrease in d13C towards the
modern day (23 out of 37). This decrease is attributable to
the addition of anthropogenically derived CO2 (13C Suess
effect) to the atmosphere. Between 1900 and 1990, the
average rate of change of the d13C in all the coral skeletons
living under open oceanic conditions is approximately
−0.01‰ yr−1. In the Atlantic Ocean the magnitude of the
decrease since 1960,−0.019 yr−1 ±0.015‰, is essentially
the same as the decrease in the d13C of atmospheric CO2
and the d13C of the oceanic dissolved inorganic carbon
(−0.023 to −0.029‰ yr−1), while in the Pacific and Indian
Oceans the rate is more variable and significantly reduced
(−0.007‰ yr−1 ±0.013). These data strongly support the
notion that (i) the d13C of the atmosphere controls ambient
d13C of the dissolved inorganic carbon which in turn is
reflected in the coral skeletons, (ii) the rate of decline in
the coral skeletons is higher in oceans with a greater
anthropogenic CO2 inventory in the surface oceans, (iii) the
rate of d13C decline is accelerating. Superimposed on these
secular variations are controls on the d13C in the skeleton
governed by growth rate, insolation, and local water
masses. Citation: Swart, P. K., L. Greer, B. E. Rosenheim,
C. S. Moses, A. J. Waite, A. Winter, R. E. Dodge, and K. Helmle
(2010), The 13C Suess effect in scleractinian corals mirror changes
in the anthropogenic CO2 inventory of the surface oceans, Geophys.
Res. Lett., 37, L05604, doi:10.1029/2009GL041397.

Complimenting modern records of tropical cyclone activity with longer historical and paleoclimatological
records would increase our understanding of natural tropical cyclone variability on decadal to centennial time
scales. Tropical cyclones produce large amounts of precipitation with significantly lower δ18O values than
normal precipitation, and hence may be geochemically identifiable as negative δ18O anomalies in marine
carbonate δ18O records. This study investigates the usefulness of coral skeletal δ18O as a means of
reconstructing past tropical cyclone events. Isotopic modeling of rainfall mixing with seawater shows that
detecting an isotopic signal from a tropical cyclone in a coral requires a salinity of ~33 psu at the time of coral
growth, but this threshold is dependent on the isotopic composition of both fresh and saline end-members. A
comparison between coral δ18O and historical records of tropical cyclone activity, river discharge, and
precipitation from multiple sites in Puerto Rico shows that tropical cyclones are not distinguishable in the
coral record from normal rainfall using this approach at these sites.

The oxygen isotropic composition (delta 18O) of coral skeletons reflects a combination of sea surface temperature (SST) and the delta 18O of seawater, which is related to sea surface salinity (SSS). In contrast, the magnesium/Calcium (Mg/Ca) ratio of a coral skeleton reflects SST independent of Salinity. by using the relationships among coral Mg/Ca ratios, coral delta 18), seawater delta 18O and SST, it is possible to determine past SST and SS uniquely. Such determinations were made and calibrated using the Mg/Ca ratio and the delta 18O of the modern part of a 3 m long coral core (Monastrea faveolata) collected from the southwest coast of Puerto Rico in the Caribbean Sea where both SST and SSS changes seasonally and the seawater delta 18O measured at the coral site....

Annually resolved coral d18O and Sr/Ca records from southwestern Puerto Rico are used to investigate
Caribbean climate variability between 1751 and 2004 C.E. Mean surface ocean temperatures in this region have
increased steadily by about 2C since the year 1751, with Sr/Ca data indicating 2.1 ± 0.8C and d18O data
indicating 2.7 ± 0.5C. Coral geochemical records from across the tropics demonstrate that regional variability is
important for understanding climate variations at centennial time scales. A strong multidecadal salinity signal in
the oxygen isotope data correlates with observed multidecadal temperature variations in the Northern
Hemisphere. Instrumental wind and precipitation data indicate that the most recent coral isotopic variations are
caused by expansion and contraction of the steep regional salinity gradient, forced by trade wind anomalies
through meridional Ekman transport. The timing of the fluctuations suggests that the multidecadal-scale wind
and surface circulation anomalies might play a role in Atlantic temperature variability and meridional
overturning circulation, but further work is needed to confirm this suggestion.

Many studies of climate variability in the
Tropical Ocean have used high-resolution chemical
tracer records contained in coral skeletons. The complex
architecture of coral skeletons may lead to the
possibility of biases in coral records and it is therefore
important to access the fidelity of coral geochemical
records as environmental proxies. Coral skeletal records
from the same coral colony, and even the same
corallite, may show large variation due to differing
extension rates, formational timing of the skeletal elements,
colony topography, and sampling resolution. To
assess the robustness of the skeletal record, we present
d13C and d18O data based on different sampling resolutions,
skeletal elements, and coral colonies of Montastraea
faveolata species complex, the primary coral
used for climate reconstruction in the Atlantic. We
show that various skeletal elements produce different
isotopic records. The best sampling rate to resolve the
full annual range of sea surface temperature (SST) is 40
samples per year. This sampling frequency also consistently
recovered SST variability measured at weekly
intervals. A sampling rate of 12 times per year recovered
84% of the annual range recording average
monthly SST changes through the year. Six samples per
year significantly decreased the ability to resolve the
annual SST range. The d18O recorded from two adjacent
colonies were very similar, suggesting that this
isotope can be trusted to record environmental changes.
The d13C, on the other hand, remained highly variable,
perhaps as a result of the activity of symbiotic algae
(zooxanthellae).

Evaristo J. Review of Use of Isotopes in Studying the Natural History of Puerto Rico. University of Pennsylvania. 2012.

Abstract:

This review summarizes the earth and environmental science research papers in Puerto Rico that used isotopic techniques between 1965 and 2011. The range of applications in isotope-related research in Puerto Rico has grown steadily, led by the ubiquitous utility of stable isotope ratios in biogeochemical (δ13C, δ15N) and ecological (δ13C, δ15N, δD) research. Moreover, research in climatology has grown in recent years, spanning from the evaluation of the fidelity of isotope records (δ18O, δ13C) as an environmental proxy to the elucidation of multidecadal variability for paleoclimate reconstructions (δ18O and Sr/Ca). On the other hand, in addition to using isotope ratios, hydrological studies in Puerto Rico have also used trace element data to answer flow source (δD, δ18O, 87Sr/86Sr) and solute source (Ge/Si) questions, as well as in examining groundwater/surface flow relationships (222Rn). Finally, various isotope data have been used in trying to understand geomorphological (10Be, δ30Si) and geophysical (Pb, Nd, and Sr) phenomena. It is hoped that this review will be able to contribute to stimulating future interests in isotope-related research as applicable in the LCZO or Puerto Rico, in particular, and/or in comparable humid tropical settings, in general.

Rainfall interception (I) was measured in 20 m tall Puerto Rican tropical forest with complex topography for a one-year period using totalizing throughfall (TF) and stemflow (SF) gauges that were measured every 2–3 days. Measured values were then compared to evaporation under saturated canopy conditions (E) determined with the Penman-Monteith (P-M) equation, using (i) measured (eddy covariance) and (ii) calculated (as a function of forest height and wind speed) values for the aerodynamic conductance to momentum flux (ga,M). E was also derived using the energy balance equation and the sensible heat flux measured by a sonic anemometer (Hs). I per sampling occasion was strongly correlated with rainfall (P): I = 0.21P + 0.60 (mm), r2 = 0.82, n = 121. Values for canopy storage capacity (S = 0.37 mm) and the average relative evaporation rate (E/R = 0.20) were derived from data for single events (n = 51). Application of the Gash analytical interception model to 70 multiple-storm sampling events using the above values for S and E/R gave excellent agreement with measured I. For E/R = 0.20 and an average rainfall intensity (R) of 3.16 mm h-1, the TF-based E was 0.63 mm h-1, about four times the value derived with the P-M equation using a conventionally calculated ga,M (0.16 mm h-1). Estimating ga,M using wind data from a nearby but more exposed site yielded a value of E (0.40 mm h-1) that was much closer to the observed rate, whereas E derived using the energy balance equation and Hs was very low (0.13 mm h-1), presumably because Hs was underestimated due to the use of too short a flux-averaging period (5-min). The best agreement with the observed E was obtained when using the measured ga,M in the P-M equation (0.58 mm h-1). The present results show that in areas with complex topography, ga,M, and consequently E, can be strongly underestimated when calculated using equations that were derived originally for use in flat terrain; hence, direct measurement of ga,M using eddy covariance is recommended. The currently measured ga,M (0.31 m s-1) was at least several times, and up to one order of magnitude higher than values reported for forests in areas with flat or gentle topography (0.03–0.08 m s-1, at wind speeds of about 1 m s-1). The importance of ga,M at the study site suggests a negative, downward, sensible heat flux sustains the observed high evaporation rates during rainfall. More work is needed to better quantify Hs during rainfall in tropical forests with complex topography.

Critical Zone (CZ) research investigates the chemical, physical, and biological processes that modulate the Earth’s surface. Here, we advance 12 hypotheses that must be tested to improve our understanding of the CZ: (1) Solar-to-chemical conversion of energy by plants regulates flows of carbon, water, and nutrients through plant-microbe soil networks, thereby controlling the location and extent of biological weathering. (2) Biological stoichiometry drives changes in mineral stoichiometry and distribution through weathering. (3) On landscapes experiencing little erosion, biology drives weathering during initial succession, whereas weathering drives biology over the long term.(4) In eroding landscapes, weathering-front advance at depth is coupled to surface denudation via biotic processes.(5) Biology shapes the topography of the Critical Zone.(6) The impact of climate forcing on denudation rates in natural systems can be predicted from models incorporating biogeochemical reaction rates and geomorphological transport laws.(7) Rising global temperatures will increase carbon losses from the Critical Zone.(8) Rising atmospheric PCO2 will increase rates and extents of mineral weathering in soils.(9) Riverine solute fluxes will respond to changes in climate primarily due to changes in water fluxes and secondarily through changes in biologically mediated weathering.(10) Land use change will impact Critical Zone processes and exports more than climate change. (11) In many severely altered settings, restoration of hydrological processes is possible in decades or less, whereas restoration of biodiversity and biogeochemical processes requires longer timescales.(12) Biogeochemical properties impart thresholds or tipping points beyond which rapid and irreversible losses of ecosystem health, function, and services can occur.